The present invention relates to an anti-counterfeit security device for documents in general.
As is known, security devices are currently inserted in many documents, such as for example bank notes; these devices are constituted by filaments with such characteristics as to increase the difficulties in reproducing these documents.
Among known security devices, mention is made of the one disclosed in European Patent No. 310,707, which in practice consists in depositing, on a support made of flexible and impermeable material, such as for example a polyester tape, regions of magnetic material, such as iron oxide, which either due to their different thickness or due to their different deposition area have, when passing beneath a magnetic head, a signal/flux directly correlated to the amount of oxide, taking into account that the filament is generally manufactured with a constant width.
It is customary to subsequently cover these regions of magnetic material with inks that are highly opaque to transmitted light, so that it is optically impossible to detect the presence and arrangement of the regions of magnetic material.
This document, viewed in reflected light, has a barely perceptible line at the filament or tape, whereas in transmitted light it is fully opaque along the same line.
These regions of magnetic material are magnetized by means of a permanent magnet which in practice charges the iron oxide so that it maintains the magnetic flux in order to be a signal-emitting element. The signals are detected by magnetic heads which, by means of appropriate electronic devices and associated programs, allow to form a decodable code, according to the thickness, density, position and/or succession of the magnetic regions.
In order to detect the magnetic flux of the regions composed using iron oxide, these regions must be moving beneath the magnetic head; this movement increases the signal as a function of the speed in a substantially proportional manner.
With this type of solution, it is not possible to detect the signal emitted by the iron oxide regions with magnetic heads if there is no relative motion between the magnetic regions and the heads.
With this kind of security element, a counterfeiter can in practice detect only its presence but is unable to detect its arrangement.
However, this security device is detectable only by means of specifically dedicated devices, and in practice cannot be detected visually, since, as mentioned above, visually it is only possible to identify the presence of a filament, without however being able to determine whether it has the required characteristics.
Another known solution uses an impermeable flexible support, constituted by a polyester tape or filament, provided with a continuous metal layer that makes said filament conductive and therefore detectable by an apparatus which, however, can only detect the presence or absence of said filament.
The metal layer has regions without metal which practice form graphic signals, for example letters or the like, which are visually perceivable and thus detectable directly without using an apparatus.
As is evident, the regions without metal, i.e. the regions that form the graphic markings, must be fully surrounded by metal in order to avoid altering the metallic continuity of the filament.
Furthermore, the metal layer can also be obtained by depositing metals through evaporation.
The document obtained by inserting the filament inside the paper has the particularity that the presence of the filament cannot be detected when it is examined in reflected light, whereas in transmitted light the graphic signals are perfectly legible.
A considerable problem for this filament is constituted by the fact that it is relatively easy to counterfeit it, since the materials required to form the metal layer and the corresponding graphic markings are normally commercially available; these counterfeits can easily deceive both personnel, when performing a visual inspection, and the equipment for detecting the presence or absence of the filament inside the document.
It is thus evident from the known art that two filaments are already known: the first one, i.e. the one provided with the magnetic regions, allows coding with a system that deposits layers with different thickness of a material which is magnetic or in any case produces a different magnetic intensity and is highly reliable both for decoding, since it is non-erasable, and for security, since it is obtained with a code, but can be decoded only with specifically provided equipment; the other filament instead can be decoded visually by personnel and can be detected by means of an apparatus that allows to check for the presence of the filament, but on the other hand can be counterfeited in a relatively easy manner.
In order to solve the above described problem, solutions have already been used commercially that in practice insert inside the document, for example a bank note, two filaments, i.e. a filament with magnetic regions ensuring absolute security against counterfeiting and a second filament allowing the personnel to visually check the document.
However, as is evident, the use of two filaments has drawbacks in the manufacture of the paper and in any case in practice provides two mutually separate elements: one that can be checked visually by personnel and the other that can be checked automatically by a device.